1. Field of the Invention
The present general inventive concept relates to an image reading apparatus and method, and more particularly to an image reading apparatus and a document supply device thereof that is capable of duplex scanning of a document.
2. Description of the Related Art
An image reading apparatus is an apparatus that is capable of converting letters or pictures printed on a document into an image signal. An image reading apparatus can be classified as a scanner, a multi-function printer having an image reading function, a fax machine, and the like.
An image reading apparatus includes a transparent document plate on which a document is positioned, and an image reading unit which is movably mounted below the document plate and scans letters or pictures of the document. The image reading unit irradiates light to the document put on the document plate, and detects the light reflected from the document to generate voltage proportional to the light intensity and convert the light intensity into a constant pixel pattern. The image reading unit includes a lamp which irradiates light, and an image sensor which receives the light reflected from the document and converts the same into an image signal. The image sensor may be configured as a charge-coupled device (CCD), a contact image sensor (CIS) or the like.
An image reading apparatus can be classified roughly as a flat bed type or a sheet feed type. A flat bed type image reading apparatus, e.g., a copying machine, is configured such that a document to be scanned is fixedly put on a flat document plate and an image sensor moves to scan the document. A sheet feed type image reading apparatus, e.g., a fax machine, is configured such that an image sensor is fixedly mounted and a document moves to be scanned sheet by sheet. Recently, an image reading apparatus adopting both flat bed type and sheet feed type has been developed.
A sheet feed type image reading apparatus requires a document supply device which automatically feeds a document to a scanning window. The document supply device includes a document supply tray on which one or more sheets of documents are loaded, and a plurality of rollers to feed the document on the document supply tray to a document discharge tray via the scanning window.
An image reading apparatus which is recently available on the market has a duplex (two-sided) scanning function where a document supply device automatically feeds a document on a document supply tray to a document discharge tray via a scanning window such that one surface and the other surface of the document sequentially pass by an image sensor. In other words, the document supply device of the image reading apparatus having the duplex scanning function feeds the document so that a first surface of the document is scanned by the image sensor while passing by the scanning window, and then reversely feeds the document having passed the scanning window and before being discharged outside so that the other surface of the document is scanned by the image sensor while passing by the scanning window.
However, because the related art image reading apparatus has a structure such that the document is reversed in a document feed path from the document supply tray to the document discharge tray, a time required to scan each sheet of document is increased or relatively long, and such an image reading apparatus can have a difficulty of accurately regulating a document feed timing when successively scanning multiple documents loaded on the paper supply tray.
Thus, there exists a need for a document feed path or a document feed timing to decrease a scanning time.